PallaPalla wasn't always evil. She and the rest of the Amazoness Quartet were in the jungle until Zirconia came and made them evil. She makes her first appearance during a solar eclipse with the Dead Moon Circus. She is responsible for the creation of the Amazon Trio-Tigers Eye, Hawks Eye, and Fish Eye.
In the Manga PallaPalla isn't as childish. She is serious about her work and rarely "messes around" with her dolls. She is an demonic little kid, in the way she looks and what she does. She tries hard and does a pretty good job at collecting dream-mirrors; she is probably the most successful of the AQ. She's destroyed by Sailor Saturn, however, and Zirconia captures her and the rest of the Amazoness Quartet in little balls.
Princess Selenity frees the Amazoness Quartet and they become the Sailor Quartet, also known as the Asteroid Senshi. The Sailor Quartet are the future guardians of Sailor Chibi-Moon when she becomes a real sailor senshi (she's one in training :p). Sailor Pallas is the equal of Sailor Mercury. She appears in the Sailorstars arc to help fight Sailor Galaxia.